This invention relates to a process for the preparation of stable, silicone-alkyd copolymers which are useful intermediates in the preparation of paints.
Alkyd resins have been used successfully as intermediates for formulating outdoor paints, however, their weatherability is poor which requires reapplication of the paints after a short period of time.
In order to improve their weatherability, alkyd resins have been modified with silicones by blending or co-reacting. Better physical properties of the co-reacted silicone modified alkyds led to the extensive use of such materials as intermediates for paints.
The trend towards the use of silicone modified alkyds resulted in a number of processes by which the silicone-modified alkyds could be co-reacted. Some of these processes have been patented.
Typically, special care must be taken in the manner in which the alkyds and the silicones are brought together in order to prevent gellation of the materials. Two step and three step processes have evolved which may be considered to be the standard by which silicone modified alkyds are prepared.
For example, Goodwin et al. in U.S. Pat. No. 2,584,340, issued Feb. 5, 1952, describes a two step process in which a silane is first co-reacted with a glycerine ester and the resulting silane-glycerine ester is further reacted with a dibasic acid or anhydride. A similar two step process is disclosed in U.S. Pat. No. 2,584,351, issued Feb. 5, 1952, wherein an organosilane is condensed with a polyhydric alcohol and the condensation product is then reacted with a polycarboxylic acid or its anhydride.
A further two step process is disclosed in British Pat. No. 740,265, published Nov. 9, 1955, wherein a mixture of a fatty acid mono-ester of a polyhydric alcohol and a free polyhydric alcohol are partly esterified by using one or more polycarboxylic acids or ester-forming derivatives of such acids. Thereafter, the remaining alcohol groups are condensed with bi- or tri-functional organosilane monomers having alkoxy groups. A similar approach can be found in Canadian Pat. No. 504,115, issued July 6, 1954.
Canadian Pat. No. 504,830 deals with a silicone modified alkyd which is prepared by pre-forming the alkyd and then co-reacting it with a silanol functional polysiloxane. Thus, there are three steps involved in such a preparation. U.S. Pat. No. 3,015,637, issued Jan. 2, 1962, deals with the type of three step reaction set forth above and in addition discloses that the condensation of the pre-formed alkyd and the polysiloxane can be enhanced by the use of titanium or zirconium compounds as catalysts.
U.S. Pat. Nos. 3,945,957 and 3,948,827, issued Mar. 23, 1976 and Apr. 6, 1976, respectively, disclose a dry planographic ink composition which is prepared from a silicone modified alkyd resin which has been prepared by pre-forming the alkyd and then condensing the alkyd with an organopolysiloxane.
Finally, there is disclosed in U.S. Pat. No. 4,069,178, issued Jan. 17, 1978, that the troublesome gellation that often occurs with the heretofore mentioned processes can be overcome by a special process wherein the major portion of the carboxylic groups which are required in the alkyd are not introduced until the final step of the process.
All of the disadvantages of the prior art methods have now been overcome by the use of the process of the instant invention whereby the ingredients necessary to form a silicone modified alkyd are all reacted together at the same time without the necessity of preforming either the alkyd or the silicone. The inventive process described below prevents the gellation problems often encountered in the above-mentioned prior art processes and yet the process provides silicone modified alkyd resins which have excellent organic solvent and water resistance in the cured form and also excellent weather resistance and gloss retention.
The resins prepared by the process of this invention have much narrower dispersity of molecular weights than the resins prepared by the prior art methods.